Buzz
Aviators rely on METAR reports to glean crucial insights into aerial conditions. While initially daunting, these reports hold a wealth of information that can be easily decoded with a bit of know-how. Upon receiving a report from an airport or meteorological center, the first step is to identify its source. Subsequent sections detail visibility, weather patterns, and other pertinent data. For assistance, consult reference charts elucidating common abbreviations to anticipate runway conditions.
Decoding the Report
Accessing a METAR report from an airport aviation center is the first step. These reports are readily available, often at no cost, irrespective of whether you're piloting an aircraft. Government aviation offices or national weather services typically offer them online. In the United States, the Aviation Weather Center provides access to reports at https://www.aviationweather.gov/metar.- To obtain a report, select your desired location from the weather center's options. You can also specify a timeframe for accessing historical reports.
Understanding Weather Codes
Decipher the initial code letters to discern the report type. METAR reports are identifiable by their initial presence in the report. Other report types exist, each conveying distinct weather information. Understanding these report types is crucial for accessing the desired weather details.
- METAR reports are issued hourly as part of routine operations.
- SPECI reports signify special, unscheduled conditions such as low visibility or thunderstorms.
- TAF reports, or terminal aerodrome forecasts, offer forecasts for specific areas and are less common than METARs.
Take note of the station identifier following the report type. The identifier, such as KAFF, denotes the station of origin. Station identifiers are assigned by the World Meteorological Organization and vary by country and station.
- For instance, KAFF represents the Air Force Academy in Colorado.
- EGLL corresponds to London Heathrow, with E indicating the UK and GLL representing Heathrow Airport.
- RJAA stands for Tokyo Narita Airport.
Examine the subsequent numbers to ascertain the report's date and time. Look for a sequence of six numbers followed by a Z, such as 212355Z. The initial pair signifies the day of the month, while the remaining digits represent the time in Zulu, equivalent to Universal or Greenwich Mean Time. Notably, the report lacks information about the month or year of issuance.
- For example, in 212355Z, 21 indicates the 21st day of the month, with the time being 2355 Zulu or 1755 MDT (Mountain Daylight Time) in Colorado Springs.
Identify a brief phrase indicating any modifications made to the report. The modifier, like COR in the example, appears after the date and time. It stands out due to its brevity and lack of numerical content, unlike preceding and subsequent codes.
- AUTO signifies an automated report.
- COR indicates a correction made by a manual observer to rectify errors in the initial automated report.
- Reports issued by personnel typically lack modifiers. Automated reports may replace human-issued ones when stations are unmanned.
Analyzing Wind and Visibility Parameters
Examine the first 3 digits of the following code for wind direction. This code, comprising alphanumeric characters, primarily denotes wind attributes. Wind direction is referenced with respect to true north, distinct from magnetic north indicated by compasses. True north can be ascertained using maps or a compass.
- In code VRB05KT, VRB indicates variable wind direction.
- Initial letters, such as 120, represent compass directions; for instance, 120 denotes southeast wind.
Utilize the remaining digits in the wind code to determine wind speed. Following wind direction, 2 or 3 digits signify wind speed in knots (KT). Occasionally, supplementary letters describe wind intensity.
- In VRB05KT, 05KT denotes wind speed of 5 knots.
- 'G' may signify gusts, as in G26KT for gusts at 26 knots.
- 'V' indicates varying wind direction for speeds exceeding 6 knots; for example, 180V260 indicates directional variance between 180 and 260 degrees.
Refer to the abbreviated wind visibility code to assess air quality. This code comprises a short series of numbers, usually with accompanying units. In the U.S., wind visibility is often measured in statute miles; for non-U.S. reports, expect visibility listed in meters.
- A visibility of 15SM implies visibility extending roughly 15 miles (24 km), or fractions like 1 1/2SM indicate 1 ½ miles.
- Visibility measured in meters may be listed as, for instance, 1400. Although units aren't specified, meters can be deduced as mile measurements typically don't exceed 30.
Scan strings beginning with 'R' for runway visibility details. Strings like R36L/2400FT provide comprehensive runway insights. Absence of such information indicates clear ground conditions.
- Initial numbers denote specific runways, with suffixes like 'L' indicating left runways in parallel setups.
- Subsequent figures represent visibility distances; for instance, /2400FT denotes visibility of 2,400 ft (730 m).
Accessing Weather and Cloud Information
View the present weather conditions if they are listed in the report. The codes following the wind information explain any significant weather conditions in the area. It can include precipitation, weather intensity, and other factors that affect navigation. There are many different signs, so consider looking up a chart to interpret the listing. For instance, try the chart at https://www.weather.gov/media/wrh/mesowest/metar_decode_key.pdf.
| Intensity | Descriptor | Precipitation | Obscuration | Other |
|---|---|---|---|---|
| - Light | MI Shallow | DZ Drizzle | BR Mist | PO Dust/Sand whirls |
| Moderate (no qualifier) | BC Patches | RA Rain | FG Fog | SQ Squalls |
| + Heavy | DR Low Drifting | SN Snow | FU Smoke | FC Funnel Cloud |
| VC In the vicinity | BL Blowing | SG Snow Grains | DU Dust | +FC Tornado or Waterspout |
| SH Showers | IC Ice Crystals | SA Sand | SS Sandstorm | |
| TS Thunderstorm | PL Ice Pellets | HZ Haze | DS Duststorm | |
| FZ Freezing | GR Hail | PY Spray | ||
| PR Partial | GS Small Hail or Snow Pellets | VA Volcanic Ash | ||
| UP Unknown Precipitation* |
- For example, you may see -SHRA. It stands for light rain showers.
- A code of +TSRA means thunderstorms with heavy rain.
Interpret the first 3 letters of the 6-digit codes to determine cloud coverage. Sky condition codes begin with 3 letters and end with 3 numbers, indicating the extent of cloud cover. A METAR report may contain multiple codes describing various cloud groups, necessitating thorough reading of the entire report.
- SKC denotes clear sky for manually-generated reports, while CLR signifies automated reports for elevations under 12,000 ft (3,700 m).
- FEW implies minimal cloud cover, spanning ⅛ to 2/8 of the sky.
- SCT indicates scattered clouds, covering ⅜ to 4/8 of the sky.
- BKN denotes broken cloud cover, with ⅝ to ⅞ of the sky obscured.
- OVC signifies overcast conditions, with complete sky coverage by clouds.
Examine the subsequent numbers to determine cloud height. These numbers indicate the base height of clouds, expressed in hundreds of feet above ground level. The presence of 'VV' denotes vertical visibility. Additionally, letters appended to the code may describe specific cloud types.
- For example, BKN220 indicates clouds at 22,000 ft (6,700 m). Simply add two zeros to determine cloud height.
- Codes like BKN220TCU denote towering cumulonimbus clouds.
- CB represents cumulonimbus clouds, often associated with storms.
- ACC signifies altocumulus castellanus.
View the combined temperature and dew point marked by a single number. These numbers, separated by a slash, denote temperature and dew point in degrees Celsius. A preceding 'M' indicates negative values for dew point.
- For instance, 15/M01 signifies a temperature of 15 °C (59 °F).
- An 'M' preceding dew point, such as M01, indicates negative values (e.g., -01).
Refer to the altimeter setting indicated by codes starting with 'A'. This code, following temperature, describes atmospheric pressure. Altimeter settings are typically listed in inches of Mercury ('Hg), or hectoPascals, aiding pilots in ensuring accurate altitude readings.
- For example, A2957 corresponds to 29.57 inches of Mercury (29.57”Hg).
- Reports commonly list altimeter settings in inches of Mercury. Non-U.S. reports may occasionally use codes like Q1030, indicating 1030 hectoPascals.
Review remarks for additional information appended to the report. The remarks section provides supplementary details deemed relevant by the reporter. These may include thunderstorm onset or cessation times, station type, air pressure, among others. Various codes may denote specific conditions, necessitating reference to a guide such as https://weather.cod.edu/notes/metar.html.
- ACSL indicates altocumulus standing lenticular clouds, while DSNT signifies distant clouds beyond 10 miles.
- SLP960 denotes sea level pressure in tenths of millibars or hectoPascals.
- Codes like SHRA DSNT N-E-SE AND DSNT NW represent moderate rain showers in distant directions.
- General numbers like 60001 55000 typically denote automated maintenance data.
- LAST COR signifies last correction, with a number indicating the correction time.
Useful Tips
- Practice by accessing METAR reports for your local airport and comparing them with actual weather conditions.
- METAR reports are globally standardized, making it easy to interpret reports from different countries.
- Approach reading METAR reports methodically, decoding each section of information one step at a time.
